Cellulose derivative manufacture



Patented May. 19, 1931 UNITED STATES PATENT OFFICE MILTON p. soHUR ANDROBERT A. WEBBER, oE BERLIN, NEW HAMPSHIRE, ASSIGNORS T BRowN COMPANY,0E BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE I CELLULO SE DERIVATIVEMANUFACTURE No Drawing.

In the manufacture of cellulose derivatives, it has been the custom toemploy vario us types of cellulosic fibers as a raw mater1al,h1gh gradecotton usually serving where pur ty and freedom from coloring matter isdesired, a wood pulp usually serving where these characteristics are ofsecondary importance. Even when wood pulp has been refined to an alphacellulose content approximating that of cotton, it has'heretofore failedto yield derivatives of a grade equal to those prepared from high gradecotton, unless special care or treatment is exercised to remove from thefiber certain impurities which survive the refimn treatment to averyslight degree but whic exert a powerful and highly undesirablecoloring effect in the preparation of'cellulose derivatives. 7

If wood pulp, for example, is examined closely, it will be observed thatit consists of units of varying fiber lengths, some bein considerablyabove and some considerably elow the average fiber length of the ulp asa whole. A considerable portion of the pulp exists in the form offibrillae, short and broken fiber,'and colloidal cellulose. We haveobserved that pulp in finely divided or colloidal condition andhereinafter designated as fines has the property of adsorbing impurit esof various kinds, tests showing that this port1on of a pulp contains farmore impurities than the'rest of the pulp. The fines are rich in resins,waxes, fats, and other impurities extractable by organic solvents,sometimes containing'over 7 of substance soluble in hotcarbon'tetrachloride. They are also high in ash content. The proportionand composition of fines in a given pulp depend upon the particularconditions and process of fiber liberation, and also upon the characterof the wood from which the pulp was derived. They are, however, alwaysdarker in color and more resistant to whitening with ,bleach than therest of the pulp. They are,

moreover, so sensitive to heat that they yellow when made into a sheetand dried on a steam drum under temperature conditions simulating pulpand paper mill practice. Owing to the fact that the impurities along thealpha cellulose are reacted upon, a cellu- Application filed July 20,

1927. Serial No. 207,314.

lose derivative prepared therefrom is dark in color and comparativelyunstable. j

In accordance with our process, these fines are removed from the pulpbefore it is converted into cellulose derivatives, as we have found thatthe quality of derivativespreparable from the resulting pulp is greatlysuperior to those preparable from the original pulp. The removal offines is advantageous in the case of the various wood pulps and othercellulosic materials employed in producing celullosic derivatives, andis especially advantageous where wood pulp is being refined to a highalpha cellulose content, as in such case the resulting pulp issubstantially equal to high grade cotton for theproduction of cellulosederivatives. Ordinarily, the impurities associated with the finestcontent of a pulp degrade it to some extent, but when fines are removedthese impurities are also removed,so that the quality of the stock andthe characteristics of the cellulose derivatives are vastly improved.

The removal of the fines may be effected at any suitable stage in thechemical processing of the pulp intended to condition it for derivative-manufacture. Preferably, however, -the fines are removed from theunbleached pulp in order to avoid their chemical processing. Processingis thus effected only upon the valuable portion of the pulp,

bleach. Where the pulp is to be refined to a high alpha cellulosecontent by a series of chemical treatments, for instance by a seneswhich includes chlorination of the unbleached pulp, followed by alkalinedigestion and by bleaching, a removal of the fines] may be effectedbefore or after any one-of it is preferable to accomplish this removalbefore the first chemical'treatment,

the chemical treatments, although in such I case, too,

suspension, and thenwashing o keted for the "manufacture of inexpensivepapers or derivatives. While unsuitable for as a saving of chemicals inall the treatments may be realized.

The removal of the fines from the pulp may be effected as disclosed inapplication, Serial No. 755 730, filed December 13, 1924, by George A.liichter and Elwood Ebie. In this process, wood pulp is washed a ainstfine mesh wire, for instance, -mesh ourdrinier wire, or against thinplates provided with perforations of, say, 0.02 inches in diameter. Thewashing may be'elfected as by repeatedly diluting the pulp with freshfiltered water to a consistency of about 1%, and then thickening thepulp by causing it to flow against the screens or plates arranged in aninclined position. Such washing results in the fines passing through thewire or plates, and the perfect fiber remaining on the screens orplates. Where unbleached wood pulp is so treated, the proportion ofmaterial passing through the screens. or plates may be from 4% to 25% ofthe weight of the original pulp. The perfectfiber may then be chemicallyprocessed as previously described, to effect its refinement to a highalpha cellulose content. The refined product is stable toward heat andlight, and yields cellulose derivatives, for example, nitrocellulose, asstable and free from coloring matter as those prepared from high gradecotton; When it is nitrated, little color is imparted to the mixednitrating acids, so that after nitration they may be fortified andreused for effecting the nitration of other pulp.

If desired, the long fibers may be separated from the pulp, the methodemployed, for instance, being-that described in application, SerialNo-.-206,477, filed July 18,1927, by Robert" A. Webber. ;,This methodinvolves passing edge-presenting members capable of picking up the longfibers, throu h the pulp andrecovering the long fibers picked up from'the edge-presenting members; ,The long .fibersf thus picked up areeminentlysnitable. forjthe .manufacture' of pure and stable"derivatives, as hereinbefore described. I

The fines obtained in our process "may, be bleached or refined andbleached, and marthe manufacture of high grade papersbecause of their,short fiber length, they are quite suitable forthe preparation ofderiva tives when high quality is not desired. This is particularly true.where these fines have been refined along with the rest of the pulp"and where color or high degree of purity in the derivatives is ofsecondary consideration,

' low price being more important. Thus,

such fines, particularly when refined, are

' suitable 'for the preparati'onof nitrocelluloses to be used in themanufacture of cheap 7 i wisadv s g novelties d the tive source of rawmaterial, where low priceis an important factor. For the preparation ofhigh grade cellulose derivatives where quality is of paramountconsideration, however, wood fiber from which the fines have beenremoved is more suitable.

By the process of the present invention, it is possible to enhancegreatly the value not only of derivatives prepared from wood fiber, butalso of derivatives prepared from cellulose fiber of other origins.Thus, we have even realized a worth-while improvement in the color ofderivatives, particularly the products of nitration, when the fines,were removed from cotton linters.

We herein do not claim the subject matter of application Serial No.202,454, filed June 29, 1927, by George A. Richter and Milton 0. Schur,which discloses a process of freeing cellulose pulp from resinousimpurities, or the product resulting from such process; nor do We hereinclaim the subject matter of application Serial No. 2l0,998, filed August5, 1927, by George A. Richter and Milton 0. Schur, and issued October 1,1929, as Patent No. 1,729,629, which discloses a process of separatingout the fraction containing fine, short, and broken fibers fromcellulose pulp, removing resinous and other impurities from thefractionseparated out, and converting the deresinified fraction intocellulose derivatives.

Having thus described our invention, it should be obvious to thoseskilled in the art that it is subject to change and modification withoutdeparting from its spirit or scope as defined in the appended claims.

What we claim is:

1. A process which comprises separatlng the finely divided and colloidalcellulose together with associated impurities from the longer fibers infibrous cellulosic materials, then converting the long fibers intocellulose derivatives.

2.} The process 5. A process'which comprises removing finelydivided andcolloidal cellulose from unbleached wood pulp, bleaching theremainwhichcomprises converting intocellulose' derivatives high alphacelluing. pulp, and converting the bleached pulp into a cellulosederivative.

6. A process which comprises removing finely divided and colloidalcellulose from unbleached wood pulp, chemically refining the remainingpulp to high alpha cellulose content, and converting it into a cellulosederivative.

7. A process which comprises removing finely divided and colloidalcellulose from unbleached Wood pulp, chlorinating, alkaline digesting,and bleaching the remaining pulp, and converting it into a cellulosederivative.

In testimony whereof we have aflixed our signatures.

MILTON O. SGHUR. ROBERT A. WEBBER.

